The invention relates to a semiconductor device having a Darlington circuit comprising a semiconductor body having two transistors comprising emitter and collector regions of the first conductivity type and an intermediate base region of the second conductivity type, the emitter region of one of the transistors, hereinafter termed "first transistor", being connected to the base of the second transistor, a diode being provided between the base and the emitter of the first transistor, a surface region of the first conductivity type which forms a first zone of the diode and is connected to the base region of the first transistor being present in said base region, a second region of the diode which forms a rectifying contact with the first zone being connected to the emitter region of the first transistor.
The object of the diode is to provide a drain for charge stored in the base of the second transistor, so that a short switching-off time is obtained. Such circuits are used, for example, in switching supply units, as well as in circuits for line deflection in television receivers.
A semiconductor device as described above is disclosed in U.S. Pat. No. 3,913,213. In this case the diode is provided by disposing a second n-type region in the p-type base of the first transistor beside the n-type emitter and forming a p-type region in said n-type region. The n-type region is connected to the base of the first transistor by means of a metal layer, while the p-type region is connected to the emitter of this transistor and to the base of the second transistor.
Experiments with such Darlington circuits have demonstrated that said circuits often do not operate satisfactorily; notably during switching off very high currents may occur, with sufficient power to cause permanent damage to the device.